Evaluation of a conditional presumed subfilter PDF model in LES of turbulent nonpremixed sooting flames

In turbulent nonpremixed flames, soot evolution is strongly affected by soot-turbulence-chemistry interactions. In particular, soot nucleation and growth happen in fuel-rich regions, and soot is then rapidly oxidized before being transported by turbulence into fuel-lean regions (in non-smoking flames). Additionally, different soot evolution processes are dominant over different mixture fraction ranges. Therefore, a presumed subfilter PDF conditioned on mixture fraction is proposed to account for this non-uniform distribution of soot in mixture fraction space. In this model, the sooting mode of the presumed subfilter PDF is locally activated only at fuel-rich mixture fraction values where growth is locally faster than the oxidation. This model is implemented within a Large Eddy Simulation (LES) framework and applied to a series of turbulent nonpremixed sooting flames. Compared to the previous unconditional presumed subfilter PDF model, the soot volume fraction values are significantly increased and in significantly better agreement with the experimental measurements.